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Proc Natl Acad Sci U S A. 2017 Jul 11;114(28):E5513-E5521. doi: 10.1073/pnas.1614857114. Epub 2017 Jun 26.

Triplet-triplet energy transfer in artificial and natural photosynthetic antennas.

Author information

1
Department of Chemistry, Yale University, New Haven, CT 06520-8107.
2
Institute of High Performance Computing, Agency for Science, Technology and Research, Singapore 138632.
3
Institute of Integrative Biology of the Cell, UMR 9891, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, CNRS, Université Paris Sud, 91191 Gif sur Yvette, France.
4
Institut de Biologie et de Technologie de Saclay, UMR 9891, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, CNRS, Université Paris Sud, 91191 Gif sur Yvette, France.
5
School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604.
6
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439.
7
Department of Chemistry, Yale University, New Haven, CT 06520-8107; victor.batista@yale.edu bruno.robert@cea.fr.
8
Institute of Integrative Biology of the Cell, UMR 9891, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, CNRS, Université Paris Sud, 91191 Gif sur Yvette, France; victor.batista@yale.edu bruno.robert@cea.fr.

Abstract

In photosynthetic organisms, protection against photooxidative stress due to singlet oxygen is provided by carotenoid molecules, which quench chlorophyll triplet species before they can sensitize singlet oxygen formation. In anoxygenic photosynthetic organisms, in which exposure to oxygen is low, chlorophyll-to-carotenoid triplet-triplet energy transfer (T-TET) is slow, in the tens of nanoseconds range, whereas it is ultrafast in the oxygen-rich chloroplasts of oxygen-evolving photosynthetic organisms. To better understand the structural features and resulting electronic coupling that leads to T-TET dynamics adapted to ambient oxygen activity, we have carried out experimental and theoretical studies of two isomeric carotenoporphyrin molecular dyads having different conformations and therefore different interchromophore electronic interactions. This pair of dyads reproduces the characteristics of fast and slow T-TET, including a resonance Raman-based spectroscopic marker of strong electronic coupling and fast T-TET that has been observed in photosynthesis. As identified by density functional theory (DFT) calculations, the spectroscopic marker associated with fast T-TET is due primarily to a geometrical perturbation of the carotenoid backbone in the triplet state induced by the interchromophore interaction. This is also the case for the natural systems, as demonstrated by the hybrid quantum mechanics/molecular mechanics (QM/MM) simulations of light-harvesting proteins from oxygenic (LHCII) and anoxygenic organisms (LH2). Both DFT and electron paramagnetic resonance (EPR) analyses further indicate that, upon T-TET, the triplet wave function is localized on the carotenoid in both dyads.

KEYWORDS:

DFT calculations; artificial photosynthesis; photoprotection; resonance Raman; triplet–triplet energy transfer

PMID:
28652359
PMCID:
PMC5514699
DOI:
10.1073/pnas.1614857114
[Indexed for MEDLINE]
Free PMC Article

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